Conventional devices for optical sensing have a photodiode (PD) in a semiconductor substrate such as silicon (Si) generally. As a solid-state imaging device, there is widely employed a planar solid-state imaging device in which PDs are two-dimensionally arranged in a semiconductor substrate and a signal corresponding to signal charges generated from each PD by photoelectric conversion is read out by a CCD or CMOS circuit. As a method of realizing a color solid-state imaging device, a general structure has color filters each of which is able to transmit only light having a specified wavelength therethrough and arranged for the color separation in a side of the light incident face of a planar solid-state imaging device. In particular, as a system which is widely employed at present for digital cameras and so on, there is well known a single-plate solid-state imaging device in which color filters which are able to transmit blue (B) light, green (G) light and red (R) light, respectively therethrough are regularly arranged on respective two-dimensionally arranged PDs.
However, in the single-plate solid-state imaging device, since the color filter transmits only light of a limited wavelength therethrough, light which has not transmitted through the color filter is not utilized, resulting in the loss of the light use efficiency. Also, with progress of high integration of pixel, the size of PD becomes the same in size as the wavelength of visible light, whereby the light is hardly guided into PD. Also, since blue light, green light and red light are detected by separate PDs adjacent to each other and then subjected to arithmetic processing, thereby achieving color reproduction, a false color may possibly be generated. In order to avoid this false color, an optical low-pass filter is necessary, resulting in the generation of an optical loss by this filter.
There have hitherto been reported color sensors in which three PDs are stacked within a silicon substrate by utilizing the wavelength dependency of an absorption coefficient of silicon and color separation is carried out due to a difference in depth on the p-n junction of each PD (see U.S. Pat. No. 5,965,875, U.S. Pat. No. 6,632,701 and JP-A-7-38136). However, such a system involves a problem that the wavelength dependency of spectral sensitivity in the stacked PDs is so broad that the color separation is insufficient. In particular, the color separation between blue and green colors is insufficient.
In order to solve this problem, there is proposed a sensor with a photoelectric conversion part on the upper side of a silicon substrate. A photoelectric conversion part detects green light and generates a signal charge corresponding thereto and blue light and red light are detected by two PDs stacked within the silicon substrate (see JP-A-2003-332551). The photoelectric conversion part on the upper side of the silicon substrate is configured to include a first electrode stacked on the silicon substrate, a photoelectric conversion layer which is made of an organic material stacked on the first electrode and a second electrode stacked on the photoelectric conversion layer. This photoelectric conversion part is configured such that when a voltage is applied between the first electrode and the second electrode, a signal charge generated within the photoelectric conversion layer transfers into the first electrode and the second electrode and a signal corresponding to the signal charge transferred into either one of the electrode layers is read out by a CCD or CMOS circuit provided within the silicon substrate or the like. In this specification, the “photoelectric conversion layer” as referred to herein means a layer capable of absorbing incident light having a specified wavelength and generating charges (electrons and holes) corresponding to the quantity of absorbed light.